I want to assert that one blank space is visible in my text.When I create a variable with one blank space, sometimes the value (blank space) is deleted. The variable was visible anymore, but without any value.

All commands that perform any kind of text assertion, perform white-space normalization on both, the input text and the assertion value. This is because browsers also normalize white-space when rendering text content in HTML.

White-space normalization in this context means that all white-space characters are replaced with a single blank space and the result is finally trimmed (white-space at the beginning and at the end are removed).

When reading and parsing the script files, white-space normalization is also performed for all command values that are known to treat with element text.

As a workaround, you might use one of the text matching strategies regexp or regexpi that interpret the assertion value as regular expression, e.g. assertText id=targetElementId regexp:\sIn case it does not matter whether the displayed text is blank or empty, a text assertion with an empty value should do it.